The present invention relates to cathode-ray tubes. More particularly, it relates to an electron gun which can enhance focus characteristics in the whole area of a fluorescent screen and in all the current ranges of an electron beam, thereby to attain a favorable resolution, and a cathode-ray tube which includes the electron gun.
In a cathode-ray tube which has, at least, an electron gun configured of a plurality of electrodes, a deflection device and a fluorescent screen, techniques as stated below have heretofore been known as expedients for obtaining a good reproduced picture in the area of the fluorescent screen from the central part to the marginal part thereof.
The techniques are, for example, one wherein an astigmatic lens is disposed within the region of electrodes (a second electrode and a third electrode) which form a focusing lens (Official Gazette of Japanese Patent Laid-open No. 18866/1978); one wherein the electron-beam apertures of the first and second electrodes of an in-line 3-beam electron gun are made vertically long, and the shapes of these electrodes are made different, or the aspect ratio of a center electron gun is set smaller than that of a side electron gun (Official Gazette of Japanese Patent Laid-open No. 64368/1976); and one wherein a rotationally-asymmetric lens is formed by a slit which is provided in the cathode side of the third electrode of an in-line arrayal electron gun, and a fluorescent screen is bombarded with an electron beam through the rotationally-asymmetric lens in at least one place, in which the depth of the slit in the axial direction of the electron gun is made greater for a center beam than for a side beam (Official Gazette of Japanese Patent Laid-open No. 81736/1985).